When Lee and Patricia Justen want to spend time with their grandson they don’t have to arrange a visit. Owen, age 8, lives just steps away, in the house behind the Justens’ home.

“He’s got two houses,” said Patricia.

On the days his mother is working, Owen just heads to his grandparents’ house, where they hang out together or take an outing, like a recent trip to the Science Museum.

“If he were far away, we’d have had to plan a week ahead,” said Patricia. “Now we do things on the spur of the moment. It’s fantastic.”

The family’s unusual living situation took root when the Justens’ daughter, Leeanne Lonson, and her husband, Rick, were expecting Owen and looking for a larger home. They found one they liked in Mendota Heights — one that came with an adjacent vacant lot at the rear of the property.

“Leeane said, ‘If we buy this, you have to build here,’ ” recalled Patricia.

At the time, the Justens were living on their family farmstead in Marystown. Lee, an organic soybean grower, had recently given up farming, and the couple were ready to try something new.

“We’re at a different stage of our life,” said Patricia. “We loved it [on the farm]. We had horses. Then the kids moved, the horses died, the dog died, and we were there alone.”

So they agreed to buy the vacant lot from their daughter and build a home. (The couple also have a son and two grandsons in North Carolina and visit there frequently.)

The Justens had already built one house, an earth-sheltered home on the farmstead. This time, they wanted a modern, energy-efficient home that would allow them to comfortably age in place, with universal design features.

“Lee’s mom lived with us for six months when she was ill,” said Patricia. “Before she died, she pointed out things that were hard for her” to navigate.

Design inspiration

To design their home, they turned to Alchemy Architects, creator of the weeHouse (small modular prefabricated housing), which they’d admired at an art museum exhibit.

“It’s environmentally friendly — less waste,” said Lee of prefab construction.

The Justens chose Alchemy’s barnHouse, a larger “farm-tech” prefab concept with an open floor plan.

“It’s the essence of house and barn all in one, with a lofty barnlike feel,” said Geoffrey Warner, founder and principal of Alchemy, St. Paul. “They didn’t need a big house, but they needed a spacious feeling.”

Warner customized the barnHouse for the Justens, with a 1,350-square-foot footprint and two angled gables. “They were looking for a flavor of modernism with more traditional forms,” he said.

Because energy efficiency was a priority for the Justens, Warner suggested SIP (structural insulated panel) construction. The thick foam-insulated panels are factory-built to order, then installed on-site.

Designing the home for the Justens’ densely wooded site was tricky because it had a steep slope down from the street. “The grade made it quite challenging to get it right,” Warner said.

But all those trees came with a bonus. Lee, a skilled woodworker and furniture maker, incorporated them into the house.

“When we cleared the lot, there were huge Chinese elm trees,” he said. “I had the wood milled, I planed and sized it, and all the trim was made from that lumber.” Wood from black walnut trees the couple had planted on their farm also was incorporated into their new home.

Working with Stinson Builders, Lee and a friend who is a retired cabinetmaker installed most of the interior wood trim and details, such as an elm bench with a live edge in the front entry. “He [Jason Stinson] let me work with the crew,” said Lee. “It was very satisfying.”

Inside, the look is spare and modern, warmed by the woodwork, and furnished with many of Lee’s handmade pieces, built to Patricia’s specifications.

“Our tastes have evolved,” she said. “We used to do all these antiques. Now we’re more modern.”

Staircase beckons

The house has a walkout lower level, designed to accommodate a live-in caretaker should that become necessary in the future.

The Justens hadn’t intended to finish the lower level right away. But the staircase Alchemy designed, with its angled wood in a latticelike pattern with half-log treads, inspired the couple not to wait.

“They are so pretty, we thought, ‘We have to be using them,’ ” said Patricia.

The lower level includes a bedroom for Owen and a workshop for Lee, as well as a bathroom and a family room.

Patricia and Lee say they love the openness of their new home, and all its custom details.

“Coffee in front of the fireplace? Walking down those stairs? Nothing better!” said Patricia.

They also love their home’s low-maintenance and energy-efficient features, including a steel-clad exterior that they’ll never have to paint, and a steel roof with solar panels that substantially reduce their energy usage and costs.

“It seems bigger than it is,” said Warner of the home. “The technology and design work together without hitting you over the head. Technology doesn’t have to scream.”

Best of all is living so close to family, the Justens say. There’s a fire pit and conversation area on the shared lot line, as well as Owen’s trampoline.

“It’s a show — they put music on, and we watch,” said Patricia. “We meet on the patio, and go back and forth. Talk about idyllic!”

Their daughter is just as enthusiastic.

“My parents are literally in my backyard,” she said. “People ask, ‘How does that work?’ It’s awesome! A perfect situation. My child gets to grow up with his grandparents. And selfishly, I love that my parents are close. It makes my heart happy.”